On Tue, 24 Feb 2015, Johannes Weiner wrote: > On Tue, Feb 24, 2015 at 07:19:24PM +0100, Michal Hocko wrote: > > Tetsuo Handa has pointed out that __GFP_NOFAIL allocations might fail > > after OOM killer is disabled if the allocation is performed by a > > kernel thread. This behavior was introduced from the very beginning by > > 7f33d49a2ed5 (mm, PM/Freezer: Disable OOM killer when tasks are frozen). > > This means that the basic contract for the allocation request is broken > > and the context requesting such an allocation might blow up unexpectedly. > > > > There are basically two ways forward. > > 1) move oom_killer_disable after kernel threads are frozen. This has a > > risk that the OOM victim wouldn't be able to finish because it would > > depend on an already frozen kernel thread. This would be really > > tricky to debug. > > 2) do not fail GFP_NOFAIL allocation no matter what and risk a potential > > Freezable kernel threads will loop and fail the suspend. Incidental > > allocations after kernel threads are frozen will at least dump a > > warning - if we are lucky and the serial console is still active of > > course... > > > > This patch implements the later option because it is safer. We would see > > warnings rather than allocation failures for the kernel threads which > > would blow up otherwise and have a higher chances to identify > > __GFP_NOFAIL users from deeper pm code. > > > > Signed-off-by: Michal Hocko <[email protected]> > > --- > > > > We haven't seen any bug reports > > > > mm/oom_kill.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > > index 642f38cb175a..ea8b443cd871 100644 > > --- a/mm/oom_kill.c > > +++ b/mm/oom_kill.c > > @@ -772,6 +772,10 @@ out: > > schedule_timeout_killable(1); > > } > > > > +static DEFINE_RATELIMIT_STATE(oom_disabled_rs, > > + DEFAULT_RATELIMIT_INTERVAL, > > + DEFAULT_RATELIMIT_BURST); > > + > > /** > > * out_of_memory - tries to invoke OOM killer. > > * @zonelist: zonelist pointer > > @@ -792,6 +796,10 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t > > gfp_mask, > > if (!oom_killer_disabled) { > > __out_of_memory(zonelist, gfp_mask, order, nodemask, > > force_kill); > > ret = true; > > + } else if (gfp_mask & __GFP_NOFAIL) { > > + if (__ratelimit(&oom_disabled_rs)) > > + WARN(1, "Unable to make forward progress for > > __GFP_NOFAIL because OOM killer is disbaled\n"); > > + ret = true; > > I'm fine with keeping the allocation looping, but is that message > helpful? It seems completely useless to the user encountering it. Is > it going to help kernel developers when we get a bug report with it? > > WARN_ON_ONCE()? >
Yeah, I'm not sure that the warning is helpful (and it needs s/disbaled/disabled/ if it is to be kept). I also think this check should be moved out of out_of_memory() since gfp/retry logic should be in the page allocator itself and not in the oom killer: just make __alloc_pages_may_oom() also set *did_some_progress = 1 for __GFP_NOFAIL. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
